If we turn around the words and definitions, itās a loop, āstainlessā does mean nothing, moreover should not be used as definition to identify the hardness of the material, as noted by āDuskā, even if there are many āstainlessā that are rust free.
Something like M340 or 16NiCr4 was used by some burrs manufacturers, but itās an old info i got years ago, nowadays i have no clue about the steel type used for.
I remain in waiting of a report from Tom about the DLC burrs, probably by glance i would say that are more similar to a Gorilla burr than a SSP HU.